A new study led by the German Institute of Human Nutrition (DIfE), a partner of the German Center for Diabetes Research (DZD), shows that gliptins – well known from diabetes treatment – may oppose the detrimental effects of fat cell accumulation in the bone marrow to improve bone healing in older, overweight patients. The research team led by stem cell researchers Thomas H. Ambrosi and Tim J. Schulz has now published its findings in Cell Stem Cell (Ambrosi et al. 2017).
It is well established that aging promotes the development of obesity. The aging process is not only accompanied by larger fat depots but also by excessive atypical fat cell accumulation in other tissue types, for example in bone marrow. As recent studies suggest, such changes are associated with loss of bone mass (osteoporosis), increased risk of bone fractures, and a disturbed maturation of the immune and blood cells in the bone marrow. In addition, other studies show that people with type 2 diabetes are particularly prone to bone fractures. The biological mechanisms underlying these observations have not been sufficiently investigated. In the present study the scientists investigated the cellular and molecular causes of these processes using cell culture experiments and studies on mice.
As the researchers show for the first time, a high-fat diet, especially in combination with an advanced age, leads to an increase of specialized (adipogenic) progenitor cells in the bone marrow, which ultimately contribute to adipocyte accumulation in the bone. Excessive bone fat not only impairs bone healing, but also hampers blood cell formation in the bone marrow of the long bones. In addition, the scientists observed that bone cell development is impaired in old age. “Our investigations thus confirm the observations of previous studies and may explain why bone fractures do not heal as well in old age, especially if the patients are overweight due to a high-fat diet,” says first author Ambrosi. “We identified a potential molecular link that mediates the negative effect of fat cells on bone tissue regeneration, the protein-cleaving enzyme dipeptidyl peptidase 4, better known as DPP4,” adds Schulz, who led the study.
This enzyme is already well known in diabetes research because it degrades hormones that regulate glucose metabolism. Its activity promotes high blood glucose levels and impairs the function of the insulin-producing cells of the pancreas. Based on these findings, pharmaceutical companies have developed various drugs, the so-called gliptins or DPP4 inhibitors, which – taken as a tablet – reduce the negative influence of DPP4 on the blood sugar level.
“Our discovery that DPP4, in addition to its influence on glucose metabolism, plays an important role in the cellular composition of bones is particularly interesting with regard to observations that people with type 2 diabetes have a tendency to sustain bone fractures,” says Ambrosi. “It points to a direct relationship between metabolic disorders and fracture susceptibility,” the scientist continues. “It also provides a novel therapeutic approach to improve the regenerative capacity of the bones by means of drugs, particularly in elderly and overweight people. It is a particular advantage that DPP4 inhibitors have been used in diabetes therapies for many years,” adds Schulz, who heads the Department of Adipocyte Development and Nutrition at the DIfE. Both agree that further research will be necessary with respect to the treatment of bone fractures using gliptins.
In addition to these investigations with immediate medical relevance, the researchers show in extensive cell-biological studies that the composition of the diet directly affects the stem cells of the bone and determines whether they form bone or adipogenic progenitor cells*. In future studies, the scientists aim to investigate how specific diets and food components can be used to support bone healing. However, the results of the study already show that people can do a lot for their bone health by following a balanced diet and by maintaining a healthy body weight, according to Schulz and Ambrosi.